Autonomous vehicles have the ability to operate without the intervention of a human operator, e.g., driver, that is, a computer controller makes decisions about accelerating, braking, and/or steering the vehicle. A vehicle may be fully autonomous or semi-autonomous. A semi-autonomous vehicle is one that is autonomous only in particular situations, for example, highway driving or parallel parking, or with respect to certain vehicle subsystems, for example, braking but not acceleration or steering.
An autonomous vehicle includes sensors for tracking an external environment surrounding the vehicle. Some types of sensors are radar sensors, scanning laser range finders, light detection and ranging (LIDAR) devices, and image processing sensors such as cameras. The controller is in communication with the sensors and uses output from the sensors to analyze the external environment, for example, defining features of a surrounding landscape, detecting roads and lanes of roads on the landscape, interpreting signs and signals, and detecting proximate objects.